during the period from 1981 to 1983, and the 1989 papers during the period from 1989 to 1991. In this interval the total number of citations increased by about 36%, reflecting, in part, the growth of activity in the field. The data in Figure C.2 are therefore normalized to the total number of citations in each period to allow better visualization of trends. The data suggest that the U.S. contribution to the total worldwide effort in AMO science is substantial and has changed little in the past decade. Europe and Japan, however, also have strong programs in AMO science.
To evaluate the ability of AMO science in the United States to respond to new opportunities and new ideas, the titles of the highly cited papers included in Figure C.1 were examined to identify ''hot topics." These were laser cooling, diode laser development, quantum chemistry/collision dynamics, femtosecond laser development, application of femtosecond lasers, and C60. Six representative papers in each area were then selected and the countries of origin of papers citing this work in the period from 1989 to 1991 examined. These are shown in Figure C.3, expressed as a percentage of the total number of citations in each area. Typically, about 56% of citations are associated with U.S.-based authors. This number is significantly higher than the approximately 40% typical of AMO science as a whole (see Figure C.2), indicating that the United States is especially strong in emergent new areas and has the resources and inventiveness to respond to new opportunities.